Method of cultivating leishmania

ABSTRACT

LEISHMANIA ARE GROWN UNDER SUBMERGED AERATED CONDITIONS IN A NUTRIENT CONTAINING GLUCOSE AND VITAMIN B1.

J I 3, 1973 I u y 6. s. ZILBERBLAT 3,743,579

United States Patent Int. Cl. C12!) 1/14 US. Cl. 195-80 1 Claim ABSTRACT OF THE DISCLOSURE Leishmania are grown under submerged aerated conditions in a nutrient containing glucose and vitamin B This application is a streamlined continuation of Ser. No. 616,934 filed Feb. 17, 1967, and now abandoned.

This invention relates to methods of cultivating Leishmania in nutrient media containing glucose and vitamin B with the use of inoculum.

Production of Leishmania is essential for making medicinal and biological preparations, viz vaccines, antigens, sera, antibiotics, etc.

Taxonomically, Leishmania belong to the type Protozoa, class Flagellata, subclass Zooflagellata, order Protomonadidae, family Trypanosomidae, genus Leishmania. The life cycle of Leishmania consists of two stages of development and is characterized by a change of hosts. Leishmania in the vertebrates grow in the leishmanial stage, while in the invertebrates they occur in the leptomonad stages. Leishmania in the leptomonad stage are causes of the human diseases known as cutaneous and visceral leishmaniasis. Said diseases are widespread in many countries of Asia, Africa and South America. To prevent and treat leishmaniasis, use is made of biological preparations which are now produced in the laboratory but require considerable improvement.

Methods of cultivating Leishmania are known wherein the inoculum is planted in a thin layer of oneor twophase nutrient media containing glucose and vitamin B which are introduced along with other known ingredients when preparing the nutrient medium. Cultivation is carried out in conditions of natural aeration of the medium.

In a nutrient medium, Leishmania develop chiefly in the leptomonad stage identical with that passed in the invertebrate host. A method of cultivating the leptomonad stage has been described in the U.S.S.R. in the journal Laboratornoye Delo, No. 6, p. 46, 1961. This method enables a maximum Leishmania concentration of 32 million per ml. to be obtained within 360 hrs. following the beginning of the development of the population in ml. of culture.

The known methods are for laboratory use. They do not give exact characteristics of the process of Leishmania cultivation, i.e. age, pH and concentration of cells in the inoculum; volume of the inoculum to be sown in proportion to the total volume of the nutrient medium; pH and Leishmania concentration in the freshly inoculated culture, and other values. In these methods, the preparation of the nutrient media involves partial destruction of some ingredients, e.g. glucose and vitamin B Thus, fractional sterilization causes decomposition of glucose to acid halfproducts unfit for consumption by microorganisms. As a result, the buffer capacity of the medium changes which often leads to a shift of the pH value of the prepared medium from a slightly alkaline reaction of 7.2-7.4 required for Leishmania multiplication to a slightly acid reaction of 6.7-6.9. Introduction of vitamin B into a slight- Leishmania in 1y alkaline nutrient medium along with other ingredients is also unfavorable, as it leads to rapid destruction of the free vitamin long before inoculation and the onset of Leishmania development. The known technique does not provide for long-term preservation of prepared media, thus necessitating reproduction of media after short intervals of time. The process of cultivation in the known methods is lengthy, requiring 240 to 360 hrs. These methods provide only a low level of maximum Leishmania concentration, ranging from 30 to 40 million per ml. Moreover, Leishmania are cultivated mostly in small volumes of nutrient media, i.e. 1 to 5 ml., which is a limiting factor in large-scale production.

The primary object of the present invention is to provide a method of obtaining Leishmania in specified amounts in stabilized nutrient media.

The above object is accomplished by providing a method of cultivating Leishmania in nutrient media containing glucose and vitamin B with the use of inoculum, wherein, according to the invention, glucose and vitamin B are introduced into the nutrient medium before inoculation with Leishmania, and cultivaiton is carried out in submerged conditions, supplying the air increasing by from 1 to 6 volumes per hour per volume of culture. It is preferable to sterilize the nutrient medium (pH 7.6-7.8) by heating at 127 C. for 1-1.5 hrs. prior to the introduction of glucose and vitamin B Glucose and vitamin B are preferably added to the nutrient medium in the form of sterile solutions. The inoculum is used in the form of culture in the leptomonad stage from the phase of logarithmic growth to the phase of diminishing growth, at the age of 5-15 days, the pH value being not lower than 5.5 and the Leishmania concentration not less than 30 million per ml. The inoculum is preferably introduced into the nutrient medium in a volume constituting 5-20% of the volume of the medium so as to obtain a Leishmania concentration of 4 to 18 million per ml. in freshly inoculated culture. Leishmania cultivation is preferably carried out at 25-28 C.

The present invention provides a Leishmania concentration of -150 million per ml., which is 3-4 times as high as that obtained by the known method of cultivation. High concentrations are developed twice as fast as in the known method. Said concentrations are obtained in cultures 500-700 times as large in volume as those in the known method. Furthermore, the invention provides for harvesting from a one-phase liquid medium Leishmania cultures in the form of a homogeneous cell suspension free from admixtures of medium ingredients, thus eliminating the necessity of additional purification of the cell material in subsequent manipulations. Separate sterilization of the nutrient medium and glucose and vitamin B solutions enables a 10-12 fold reduction in the time required for preparing nutrient media, reducing it to several hours. Separate storage of the nutrient medium and glucose and vitamin B solutions insures maintenance for several months of specified concentrations and a high quality of said ingredients in a medium ready for inoculation which is used when required. The present method is applicable for cultivating Leishmania of the cutaneous and visceral types.

For a better understanding of the present invention by those skilled in the art, the following examples are given by way of illustration.

EXAMPLE 1 Leishmania in the leptomonad stage of development are cultivated in a 5-liter reactor in a two-phase peptoneyeast medium of the following composition (ingredients calculated for 1 liter of medium):

DD-peptone ml 200 Meat broth (0.5 kg. of beeg boiled in 1 l. of

water) ml 200 Distilled water rnl 600 Dry granulated blood g- 20 Na2HP04-12H2O g 3 KH PO g. 0.5

The nutrient medium is prepared in the reactor. First, a hematin solution is prepared from dry granulated swine blood. For this purpose hematin is extracted from 100- g. of blood granules with alkaline water at a pH of 8.3- 8.4. The hematin solution is sterilized by heating at 127 C. for 1.5 hrs. Broth containing phosphates is added to said solution and the pH adjusted to 7.6-7.8. The nutrient medium is sterilized by heating at 127 C. for 1.5 hrs. The medium is then cooled to 15-25 C. and divided into two portions. One portion is used for cultivating Leishmania. For this purpose solutions of 150 ml. of 34% sterile glucose and 5 ml. of 5% sterile vitamin B are added to it and thereafter inoculation is carried out. The other, greater, portion is stored at the above temperature for use over a period of several months.

The inoculum used must be a culture containing not less than 97% Leishmania in the leptomonad stage of development (whereof the permissible amount of deformed cells shall not exceed 5%) and not more than 3% Leishmania in the leishmanial stage of development. The pH of the inoculum shall be not less than 5.5, the concentration of microorganisms 30 million or more, and the age of the culture 5 to 15 days. Inoculation is carried out in the phase of logarithmic growth at a rate of 5-20% of the volume of the nutrient medium. The inoculum is primarily grown in matrass flasks and then, successively, in vessels of 05-1-5 liters. The culture grown in each vessel serves as the inoculum for a culture of an identical or greater volume.

The Leishmania concentration in a freshly inoculated culture is 4 to 18 million per ml., the pH being 7.2-7.8.

After inoculation the vessel containing the culture is placed in a thermostat or heated so as to provide for Leishmania development a temperature of 25.5-27.5 C.

The freshly inoculated culture is aerated with increasing volumes of air. During the first 24 hrs. the air flow rate is 1 volume per hr. per 1 volume of culture. The flow rate is then gradually increased to 2.7 volumes per hr. per 1 volume of culture for the next 24 hrs. For the third time, the flow rate is increased to 6 volumes per hr. per 1 volume of culture. The maximum flow rate is maintained until the concentration of Leishmania in the culture reaches the maximum. The duration of a cycle of Leishmania cultivation in a volume of 3.5 liters requires 144-168 hrs. During this period the cell concentration rises from the initial value of 4-18 million per ml. to the final value of 120-150 million per ml.

EXAMPLE 2 Leishmania in the leptomonad stage of development are cultivated in a 5-liter reactor in a one-phase peptoneyeast medium of the following composition (ingredients calculated for 1 liter of medium):

DD-peptone ml 200 Meat broth (0.5 kg. of beef boiled in 1 l. of

water) ml 200 Hematin solution ..ml.. 200 Distilled water ml 400 NflzHPOLylZHgC) g 3 KH2PO4 .g

Hematin solution is prepared for which purpose 500 ml. of distilled water alkalized with 20% NaOH to a pH of 8.3-8.4 are added to 20 g. of dry granulated swine blood. This mixture is sterilized at 127 C. for 1.5 hrs. after which the blood granules become a finely dispersed suspension. Said suspension is then cooled to 20-30" C. and left to precipitate at 4-8" C. for 1-3 days after which the supernatant liquid is decanted or the mixture is filtered. The resulting transparent filtrate of dark violet color is used as hematin solution for preparing the nutrient medium. This solution can be preserved for a month at a temperature of 4-6 C. by adding 1% of chloroform to it.

The nutrient medium is prepared in a reactor by mixing the hematin solution with broth containing phosphates. The pH is adjusted to 7.6-7.8. Further preparation of the nutrient medium, collection of the inoculum, inoculation of Leishmania and submerged cultivation by supplying air to the culture in increasing volume are carried out as described in Example 1.

The graph presents curves of Leishmania development in different nutrient media. Curve 1 shows the development of Leishmania in classical medium of NNN agar with enriching liquid containing 1% peptone. Curve 2 shows the development of Leishmania in conventional two-phase peptone-yeast medium. Curve 3 shows the development of Leishmania in a one-phase peptone-yeast medium according to the method described in Example 2. In the graph, days of culture growth are plotted on the axis of abscissae, while Leishmania concentrations in million per ml. are given on the axis of ordinates.

It will be apparent from the graph that the maximum Leishmania concentration in the present method (Curve 3), i.e. 200 million per ml., obtained on the 6th day of cultivation, is 6 times as high as that obtained by the known method Curve 2), while the time required for achieving this concentration is reduced by half.

Though the present invention has been described in accordance with a preferred embodiment, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope thereof.

These changes and modifications are to be considered as falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of cultivating Leishmania of the cutaneous and visceral types in a nutrient media, said method comprising preparing a liquid nutrient medium, containing nitrogen sources, growth factors and mineral salts, adding glucose and vitamin B to the prepared nutrient medium, introducing an i-noculum which is Leishmania culture at the age of 5-15 days of growth in the leptomonad stage of development in the phase of logarithmic growth of the population at a pH of the culture of not less than 5.5, in an amount such as to insure a starting concentration of Leishmania in the freshly inoculated culture of from 4 to 18 million Leishmania per ml., and cultivating the Leishmania at a temperature of 25 to 28 C. in submerged conditions, with air being supplied thereto in increasing volumes from 1 to 6 volumes per hour per one volume of culture.

References Cited Trager: J. Protozool., vol. 4, pp. 269-276 (1957).

ALVIN -E. TANENHOLTZ, Primary Examiner US. Cl. X.R. 195-104, 

